3-mode blended fibers in an engineered cementitious composite

ABSTRACT

Disclosed herein are fiber reinforced cement composite materials incorporating a 3-mode fiber blend that includes cellulose pulp and synthetic fibers in a ratio selected to provide the composite material with improved water absorption characteristics and the same or improved mechanical properties as compared to equivalent composite materials reinforced with predominantly or all cellulose fibers. Also disclosed herein are fiber blends comprised of a combination of cellulose fibers and polypropylene fibers adapted to reinforce cementitious composite articles manufactured by the Hatschek process and autoclave cured.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Application No. 61/485,280 filed on May 12, 2011,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present disclosure relate to cementitious compositematerials incorporating reinforcement fibers with improved propertiesdeveloped primarily for use in the building and construction industry.

2. Description of the Related Art

Fiber reinforced cementitious composite materials have been widely usedin building construction. Cellulose fibers, in particular, have beenused to reinforce various fiber cement building products because theyimpart favorable properties to the building product. Moreover, cellulosefibers have a unique microstructure with unique physical and mechanicalproperties that are suitable for the Hatschek process, the preferredcommercial process for manufacturing fiber cement sheets and panels. Forexample, the micro-fibrils in cellulose fibers help to build aneffective filtration system to catch the fine particles in the fibercement slurry to form a thin fiber-particle film during the Hatschekprocess. The micro-fibrils also branch out with the branches functioningas anchors in the cured fiber cement composite thereby enhancing thebonding at the interface between the fibers and cementitious matrix.

However, there are also disadvantages associated with using cellulosefibers to reinforce cementitious building products. For example, thechemical composition and large surface area of the micro-fibrilstructure of the cellulose fibers render the fibers highly hydrophilic.The hydrophilic nature of cellulose fibers can increase water absorptionof the fiber cement composite, which can result in some performanceissues. Furthermore, cellulose fibers are generally more water sensitiveand less alkali resistant. Therefore they can experience progressivedegradation over time.

While synthetic fibers have been used to reinforce cementitiouscomposite materials, prior art products reinforced with synthetic fibersnot only require a much longer manufacturing cycle but also have lessthan desirable mechanical properties as compared to products reinforcedwith cellulose fibers. For example, fiber cement composites reinforcedwith synthetic fibers have been typically limited to the air cureprocess because synthetic fibers tend to disintegrate at hightemperature conditions of the autoclave process that is commonly usedfor curing cellulose fiber reinforced cement composites. The air cureprocess takes much longer, normally 28 days, as compared to theautoclave cure process, which usually takes less than 3 days.Replacement of cellulose fibers with synthetic fibers can also result inlower flexural strength of the fiber cement composite due to the lowerfiber-matrix interface bonding. Moreover, non-cellulose fibers cancreate added difficulties in manufacturing using the Hatschek process.Accordingly, there is a need for improved reinforcement fibers that canimpart desirable mechanical properties to cementitious composites andare also compatible with the Hatschek process and autoclave curing.

SUMMARY OF THE INVENTION

The compositions, materials, articles, and methods of manufacture ofthis disclosure each have several aspects, no single one of which issolely responsible for its desirable attributes.

Any terms not directly defined herein shall be understood to have all ofthe meanings commonly associated with them as understood within the art.Certain terms are discussed below, or elsewhere in the specification, toprovide additional guidance to the practitioner in describing thecompositions, methods, systems, and the like of various embodiments, andhow to make or use them. It will be appreciated that the same thing maybe said in more than one way. Consequently, alternative language andsynonyms may be used for any one or more of the terms discussed herein.No significance is to be placed upon whether or not a term is elaboratedor discussed herein. Some synonyms or substitutable methods, materialsand the like are provided. Recital of one or a few synonyms orequivalents does not exclude use of other synonyms or equivalents,unless it is explicitly stated. Use of examples in the specification,including examples of terms, is for illustrative purposes only and doesnot limit the scope and meaning of the embodiments herein.

One embodiment of the present disclosure provides a fiber cementcomposite material incorporating a novel fiber blend (3-mode blend)adapted to reinforce and improve the mechanical properties of thecomposite material. The fiber cement composite material includes about10%-80% by weight cementitious binder, about 20%-80% by weight silica,about 0%-50% by weight density modifier, about 0%-10% additives, andabout 0.5%-20% by weight a 3-mode fiber blend that includes refinedcellulose fiber, unrefined cellulose fiber and synthetic fibers. Therefined cellulose fiber is normally shorter with a length of 0.8 to 2.0mm and high surface areas. The unrefined cellulose fiber has a length of1.5 to 3.0 mm with medium surface areas. The synthic fiber has longerfibers and lowest surface areas. The refined cellulose fiber accountsfor 50 to 75% of the total fiber mass or population. The unrefinedcellulose fiber accounts for 10 to 25% of the total fiber mass orpopulation while the synthetic fiber is about 10 to 25% of total fibermass or population. In one implementation, the ratio of cellulose fibersto synthetic fibers in the fiber blend is between 3 and 24, morepreferably between 4 to 12. In another implementation, the syntheticfibers comprise polypropylene (PP) fibers. In another implementation,the synthetic fibers consist essentially of PP fibers. The PP fibers arepreferably fibrillated with irregular forms. In some implementations,the PP fibers have an average length of between 4 to 15 millimeters(mm), preferably 6 to 12 mm In some other implementations, the fibercement composite material comprises about 3% to 10% by weight cellulosefibers and about 0.25% to 2% by weight PP fibers, or preferably 0.5% to1.5% by weight PP fibers.

In other implementations, the fiber blend includes three modes of fiberlength distribution. One mode can comprise refined shorter cellulosefibers. A second mode can comprise unrefined cellulose fibers. A thirdmode can comprise long PP fibers. Preferably, the average length of therefined shorter cellulose fibers is less than the average length of theunrefined cellulose fibers; and the average length of the PP fibers islonger than the average length of the unrefined cellulose fibers. In oneimplementation, one mode can comprise about 50% to 80% refined shortercellulose fibers having an average length of less than or equal to 2 mm.A second mode can comprise about 10% to 25% unrefined cellulose fibershaving an average length of greater than or equal to 2 mm, preferablybetween 2 mm to 2.5 mm. A third mode can comprise about 10% to 25% longPP fibers having an average length of between 4 mm to 15 mm. In yet someother implementations, the PP fibers are engineered with a hydrophilicsurface and a hydrophobic bulk part to form fiber cement grade PPfibers. In one embodiment, the fiber reinforced composite materialspreferably has a moisture movement (MM) of less than 0.5%. In anotherembodiment, the material have a moisture movement of at least 25% lessthan that of an equivalent fiber cement material.

Another embodiment of the present disclosure provides a fiber reinforcedcement composition comprising a hydraulic binder, aggregates, cellulosefibers, and polypropylene fibers. Preferably, the polypropylene fibershave irregular forms. In one implementation, the ratio of the weightpercent of cellulose fibers to polypropylene fibers is between 3 to 24,preferably between 4 to 12. In another implementation, the compositioncomprises about 2% to 10% by weight cellulose fibers and about 0.25% to2% by weight polypropylene fibers. In another implementation, the fiberreinforced cement composition is adapted for forming exterior wallsidings.

Yet another embodiment of the present disclosure provides a method ofmanufacturing a fiber reinforced cementitious article suitable for thehatschek process and autoclave curing. The method includes the steps offorming a fiber cement slurry which can comprise a hydraulic binder,aggregates, water, cellulose fibers and polypropylene fibers; depositingthe fiber cement slurry on a plurality of sieve cylinders that arerotated through the fiber cement slurry wherein the cellulose fibers andpolypropylene fibers filter the fiber cement slurry to form a thin fibercement film. The method further includes the steps of transferring aseries of sequential layers of the thin fiber cement films to a felt soas to build a thicker fiber cement layer; removing water from thethicker fiber cement layer; transferring and winding the fiber cementlayer onto a size roller to achieve desired final thickness; cutting andunwinding fiber cement sheet onto a conveyor; and curing the fibercement sheet in an autoclave at a temperature of at least 150° c. Insome implementations, the method further includes the step of formingthe autoclave cured fiber cement sheet into a building constructionpanel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are photos of two different types of synthetic fibers afterthe Parr bomb test according to certain embodiments of the presentdisclosure.

FIGS. 2A-2B are photos illustrating examples of synthetic fibers in acement matrix according to certain preferred embodiments before theautoclave cycle under a microscope.

FIGS. 3A-3C are various views of the synthetic fiber shown in FIGS.2A-2B in the fiber composite matrix.

FIG. 4 is a chart showing the moisture movement of various fiber cementcomposite material samples made in accordance with certain preferredembodiments as compared to controls.

FIG. 5 is a chart showing the water absorption values of fiber cementcomposite material samples made in accordance with certain preferredembodiments compared to the control formulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Disclosed herein are fiber cement articles reinforced with a fiber blendpre-selected to provide the fiber cement articles with improvedmechanical and/or chemical physical properties. Also disclosed hereinare fiber blends comprised of synthetic and natural fibers atpre-selected ratios for reinforcing cementitious composite materials andmethods for manufacturing. Also disclosed herein are synthetic andcellulose fiber blends adapted to reinforce cementitious compositearticles manufactured by the Hatschek process and autoclave cured. Alsodisclosed herein are fiber reinforced cement formulations that includecellulose pulp and synthetic fibers in a ratio selected to provide abuilding material with improved water absorption characteristics and thesame or improved mechanical properties as compared to equivalentbuilding materials reinforced with predominantly or all cellulosefibers.

One of the challenges in incorporating synthetic reinforcing fibers,such as polypropylene (PP) fibers, in fiber cement composite materialsis that synthetic fibers, unlike cellulose fibers, are not configured tocatch sufficient amount of fine particles in fiber cement slurry to forma thin fiber cement film during the Hatschek process. Additionally, mostsynthetic fibers like PP fibers will disintegrate at elevated autoclavetemperatures. As such, while synthetic fibers have been incorporated infiber cement articles, the synthetic fibers are not successfully addedin sufficient quantities as a substitute for substantial amounts ofcellulose fibers, especially not in fiber cement panels and sheets thatare typically manufactured by the Hatschek process and autoclave cured.The inventors have developed certain fiber reinforced composite materialcompositions that incorporate fiber blends comprising synthetic andcellulose fibers selected to reinforce cementitious articlesmanufactured by the Hatschek process and cured at elevated autoclavetemperatures without deleterious effects.

Fiber Blends

Various embodiments of the present disclosure provide novel 3-modeblends of synthetic and cellulose fibers that can be incorporated in acementitious composition for reinforcing composite materials formed bythe Hatschek process and cured at elevated autoclave temperatures. Incertain preferred embodiments, the synthetic fibers includepolypropylene (PP) fibers that are engineered with certain properties.In one embodiment, the PP fibers have a high degree of crystallinity,high linear density, and high thermal resistance. In someimplementations, the PP fibers have a linear density of at least2.2±0.22 dtex and a high thermal resistance. In one embodiment, the PPfibers are engineered to have a high melting point and narrow molecularweight distribution to survive the high temperatures. In someimplementations, the PP fibers have length of between 4 to 15millimeters (mm), preferably between 6 to 10 mm of mono-filaments insome embodiments. The PP fibers can be mono-filament or fibrillated withdifferent shapes, including circular or irregular forms. Thecross-section of the PP fibers can have eccentric sheath core orconcentric sheath core, hollow splittable, zigzag, wavy, or spiraltypes. The irregular shapes can help for improving the mechanicalinterlocking bonding to resist fracture of the fiber cement. Theirregularity of the PP fiber surface of various preferred embodimentswill help the PP fibers to be caught on the filter drum for filmformation during the Hatschek process.

To improve the affinity between PP fibers and cement, the PP fibers ofsome embodiments of the present disclosure may be modified to have ahydrophilic surface while leaving the bulk part of PP fiber hydrophobicto produce a fiber cement grade PP fiber. In some embodiments, the PPfiber surface is made hydrophilic by first chemically altering the fibersurface layer and followed by depositing an extraneous layer on top ofthe altered fiber surface layer, thereby generating a sharp interface.Given the non-reactive character of the PP fiber surface, the PP fibersrequire generating high energy species, such as radicals, ions,molecules in excited electronic states, etc. Coating physical treatmentinvolves itself in the generation, usually by high-energy methods, ofmatter fundamentals, such as atoms or atomic clusters, to be depositedon material surfaces. Such treatments for modification include flame,corona, cold plasma, hot plasma, UV, laser, electron beam, ion beam, andsputtering. Impregnation of PP fiber with surfactants is an example ofthe additional layer on the PP fibers surface.

In some embodiments, the PP fiber surface is made hydrophilic by wettreatment such as covalent attachment of polymer chains. Wet treatmentmay include exposing the PP fiber surface to oxidizing wet chemicalssuch as chromic acid, nitric acid or potassium permanganate to result ingeneral oxidation, forming carbonyl groups, hydroxyl groups andcarboxylic acid groups on the polymer surface. The covalent attachmentof polymer chains to the PP fiber surface can be achieved by eithergraft polymerization or polymer grafting after the pretreatment with UV,electron beam, and γ-ray irradiation.

The PP fibers of preferred embodiments can be supplied in a bundle form.Appropriate dosing and mixing procedures and equipment can be used toensure proper dispersion of the fibers, although the surface of thefibers may have been modified to be hydrophilic.

The PP fibers are preferably blended with cellulose fibers atpreselected ratios for optimum performance. In one embodiment, thepercent by weight ratio of PP fibers to cellulose fibers in a fibercement composition is between 3 to 24, or between 4 to 12. The cellulosefibers preferably have a length between 0.5 to 3 mm. The micro-fibrilstructures in the cellulose fibers are suitable for filtration process,which in turn are good for film formation on the filter drum in aHatschek process. PP fibers in monofilament form have poor capability ofcatching fine particles from film formation. Well blended PP fibers andcellulose fibers according to preferred embodiments of the presentdisclosure will build an inter-penetration fiber network, which in turnprovides good film formation in the Hatschek process.

FIG. 1A is a photo showing high crystalline PP fibers according oneembodiment of the present disclosure. FIG. 1B is a photo showing ageneral commercial PP fiber. The PP fibers in both FIGS. 1A and 1B areshown after the Parr bomb test, which simulates elevated autoclavecuring condition for the fiber cement materials. The bomb cell (part Noat 4744 with total capacity at 45 ml) is from Parr Instrument Company.Weight at 0.5 grams of synthetic fiber is put in the PTFE cup withpre-filled 25 ml of water with pH at 13. The synthetic fiber issubmerged inside the water, which may float onto the water top surface.The PTFE cover is put back and sealed inside the bomb body. The bombwith sample is put in the oven at 160C and left inside for 15 hrs beforecooling down to room temperature. The bomb body is opened for fiberdamage study under microscopy after cooling down to room temperature.The high crystalline PP fibers still retained good fiber integrity whilethe commercial PP fibers broke into pieces and slightly melted together.Thus, the high crystalline PP fibers can survive the autoclave for theshort hydration process time with increased temperatures.

In some embodiments, the fiber blend comprises three modes of fibers.The fiber blend includes a combination of refined shorter cellulosefibers, preferably between 0.8 mm to 2 mm with highest surface areas;unrefined cellulose fibers, preferably between 2 mm to 2.5 mm withmedium surface areas; and long PP fibers, preferably between 4 mm to 15mm with lowest surface areas. The combination of the three modes offibers helps to achieve balanced product performance in Modulus ofRupture (MOR), toughness and nailablity. In some implementations, thefiber blend comprises about 50 to 80% refined shorter cellulose fibers,about 10 to 25% unrefined cellulose fibers, and about 10 to 25% long PPfibers.

Fiber Cement Compositions

One preferred composition of the fiber reinforced composite materialcomprises a cementitious binder, aggregates, optional density modifier,optional various additives, and a fiber blend comprising cellulosefibers and PP fibers adapted to improve various material properties. Itwill be appreciated that not all of these components are necessary toformulate a suitable building product, and thus, in certain embodiments,the formulation may simply comprise cementitious binder and blendedfibers.

The cementitious binder is preferably Portland cement but can also be,but is not limited to, high alumina cement, lime, high phosphate cement,and ground granulated blast furnace slag cement, or mixtures thereof.The aggregate is preferably ground silica sand but can also be, but isnot limited to, amorphous silica, micro-silica, diatomaceous earth, coalcombustion fly and bottom ash, rice hull ash, blast furnace slag, steelslag, mineral oxides, mineral hydroxides, clays, magnasite or dolomite,metal oxides and hydroxides, and polymeric beads, or mixtures thereof.

The density modifiers can be organic and/or inorganic lightweightmaterials with a density less than 1.5 g/cm³. The density modifiers mayinclude plastic materials, glass and ceramic materials, calcium silicatehydrates, microspheres, and volcanic ashes, including perlite, pumice,shirasu basalt, and zeolites in expanded forms. The density modifierscan be natural or synthetic materials.

The additives can include, but are not limited to, viscosity modifiers,fire retardants, waterproofing agents, silica fume, geothermal silica,thickeners, pigments, colorants, plasticizers, dispersants, formingagents, flocculents, drainage aids, wet and dry strength aids, siliconematerials, aluminum powder, clay, kaolin, alumina trihydrate, mica,metakaolin, calcium carbonate, wollastonite, and polymeric resinemulsion, and mixtures of thereof or other materials.

The cellulose fibers in the fiber blend can be unrefined/unfibrillatedor refined/fibrillated cellulose pulps from various sources, includingbut not limited to bleached, unbleached, semi-bleached cellulose pulp.The cellulose pulp can be made of softwood, hardwood, agricultural rawmaterials, recycled waste paper or any other forms of lignocellulosicmaterials. Cellulose fibers can be made by various pulping methods. Inthe pulping process wood or other lingocellulosic raw materials such askenaf, straw, and bamboo are reduced to a fibrous mass by the means ofrupturing the bonds within the structure of lignocellulosic materials.This task can be accomplished chemically, mechanically, thermally,biologically, or by combinations of these treatments.

The synthetic fibers in the fiber blend can be of any type including,but not limited to, glass fibers, polyester, polypropylene, aromaticpolyamide, and acrylic fibers. These types of fibers can be made to beused in a composite product that is air cured or treated in such a wayas to be able to survive a higher temperature autoclave cycle. Anexample of such a fiber can be found as described in U.S. Pat. No.6,010,786 (Takai).

In one embodiment, the fiber cement composition comprises about 10%-80%by weight cementitious binder; about 20%-80% by weight silica(aggregates); about 0%-50% by weight density modifier; about 0%-10% byweight additives; and about 0.5%-20% by weight of fiber blend comprisingcellulose fibers and PP fibers. In one implementation, the fiber cementformulation comprises about 4.5%-9% fiber blend. In anotherimplementation, the fiber blend comprises 3%-10% cellulose fibers, orpreferably 4%-8% cellulose fibers based on total mass of dry mix.

In another embodiment, which is particularly suitable for autoclavecuring, the formulation comprises about 20%-50% cement; about 30%-70%ground silica; about 0%-50% density modifiers; about 0%-10% additives;and about 2%-10% fiber blend comprising cellulose fibers and PP fibers.

Substitution of Cellulose Fibers with Pre-selected PP Fibers

Certain preferred embodiments of the present disclosure are directed tosubstituting a fraction of the cellulose fibers in a fiber cementcomposition with PP fibers, preferably fiber cement grade PP fibers, toreduce the moisture absorption of the resulting product withoutdetrimentally affecting other properties. In one embodiment, up to 50%of cellulose fibers in a fiber cement composition can be substitutedwith fiber cement grade PP fibers. In some implementations, the fibercement composition includes 0.5% or more hydrophobic polypropylene (PP)fibers as well. The fiber blend will provide the balanced benefits ofcellulose and PP fibers in which cellulose fibers serve as processingaids, density modifier and reinforcement, while PP fibers are used asthe secondary reinforcement to enhance the toughness. The watersensitivity of the formed composite will be significantly reduced.

In some embodiments, by replacing up to about 50% of the cellulosefibers with variable lengths distributed between 0.8-3.0 mm with theaddition of a small amount of hydrophobic PP fibers, the hydrophilicproperty of the fiber cement slurry and composites can be significantlyreduced while the film formation capability in the Hatschek process isstill maintained. The long term performance or reinforcement of theblended (PP and cellulose fibers) fiber cement composite is retained bythe stability of the PP fibers. The length of the PP fibers can beengineered to suit different reinforcement requirements. For example,shorter and high surface area fibers may improve strength of thecomposite, while longer fibers can make the composite more ductile

FIGS. 2A and 2B are photos taken under polarized light of a fiber blendincorporated in a cementitious formulation according to certainpreferred embodiments of the present disclosure. The fiber blendcomprises fiber cement grade PP fibers and cellulose fiber. As shown inFIGS. 2A and 2B, the mixture of PP and cellulose fiber was dispersedvery well within the inter-network structure.

FIGS. 3A-3C are photos showing a fiber cement composition reinforcedwith a fiber blend according to one embodiment after elevated autoclavecuring. The fiber blend comprises a mixture of PP fibers and cellulosefibers. As shown in FIG. 3A, the PP fibers remain fully intact afterautoclave curing. FIG. 3C shows that upon sample breaking, the PP fibersdid not break and pulled out on the sample matrix surface, which isdifferent from that of cellulose fibers as shown in the photo in FIG.3B. This observation is consistent with the fact that PP fiber is moreductile than that of cellulose. Moisture movement (MM) in the preferredembodiments has shown a surprising reduction compared to control samplesin post carbonation measure. After carbonation, samples were tested andthe moisture movement was reduced to a level that showed vastimprovements over the control samples FIG. 4 shows the moisture movementfor the present disclosure in samples (3-6) and the controls (1-2).Samples (3-6) were made in accordance with the fiber cement formulationsdisclosed herein. As shown, samples made according to the preferredembodiments had less moisture movement than the control samples, withthe improvement of up to about 21%. The reduction in moisture movementcan inhibit propagation of joint spacing and cracking around nails whenthe products are in service.

Water absorption coefficient (WAC) is also shown to be significantlyreduced in the preferred embodiments. FIG. 5 shows the water absorptioncoefficient for the samples (5-6) and the control (1). As shown, thereis about 41% improvement for the invention samples over the control. Thelower water absorption values lead to a more durable fiber cementproduct. It has been found that a decrease in water absorptionproperties transfers into better performance in freeze thaw andshrinkage of the building material. The WAC test method is based on ISO15148:2002(E). Cellulose pulp was tested at from 4 to 6% and thepolypropylene fiber was tested at from 0.25 to 1.5% in variouscombinations. On the lower end of the fiber combinations, 0.25-0.50% PPfiber with 4.5% cellulose fiber did not provide enough reinforcement inthe form of strain property. On the upper end of using 1.5% PP fiber and6% cellulose fiber, it was found that the water absorption improvementsdid not further improve while the cost increased significantly. It wasfound that at least 5% cellulose fiber is needed to achieve the requiredstrain to form a durable product. The initial screenings of a filter padformulations showed similar results to the properties andcharacteristics of the scaled up Hatschek process formulations that ledto the final blend of fibers that provided a composite product that wascomparable to an all cellulose fiber composite product.

With an overall total reduction in fiber content, and more specificallycellulose fibers, it has been found that water absorption and moisturemovement properties have improved leading to increased overalldurability of the fiber cement composite. The 3-mode blended fibercomposite maintains many of its physical properties as well and providesincreased drainage on the process side which makes the Hatschek machinerun faster and with less load. While density is increased slightly dueto reduction of fiber content, nailability and strength of the productare acceptable for installation. No predrilling is required of theblended composite product.

Moisture movement (MM) in the preferred embodiments has shown asurprising reduction compared to control samples in post carbonationmeasure. After carbonation, samples were tested and the moisturemovement was reduced to a level that showed vast improvements over thecontrol samples. In FIG. 4, it can be seen that the reduction inmoisture movement in Examples 1, 2, 3, and 4 of the blended compositescompared to the control samples.

Other preferable formulations can be seen in the Examples in Table 1below.

TABLE 1 Summary of Properties MOR Density WAC (back) MM Example Mpa g/cckg/m²*sec{circumflex over ( )}0.5*1000 % Nailability 1 Par Par 10.080.58 Excellent (Control) 2 Par Par 17.63 0.51 Excellent (Control) 3Better Higher 14.44 0.48 Excellent 4 Better Higher 12.05 0.49 Very Good5 Par Higher 5.91 0.46 Very Good 6 Better Higher 6.04 0.48 Very Good

TABLE 2 Summary of Properties I MOR Density WAC (back) MM Example Mpag/cc kg/m²*sec{circumflex over ( )}0.5*1000 % Nailability 1 Par Par10.08 0.58 Excellent (Control) 5 Par Higher 5.91 0.46 Very Good 6 BetterHigher 6.04 0.48 Very Good

TABLE 3 Summary of Properties II MOR Density WAC (back) MM Example Mpag/cc kg/m2*sec{circumflex over ( )}0.5*1000 % Nailability 2 Par Par17.63 0.51 Excellent (Control) 3 Better Higher 14.44 0.48 Excellent 4Better Higher 12.05 0.49 Very Good

Density of the blended composites has shown an increase as can be seenin Tables 2 and 3 above. Table 2 shows formulation examples with a lowerdensity modifier while Table 3 shows formulations that do not contain adensity modifier. The nailing test results provided values that werecomparable to the control samples. The mechanical properties showdurability of the product and installation soundness that provide acomposite that can replace current fiber cement products at a reducedraw material cost while not suffering a decline in performance. The MOR,density, and MM tests were done according to ASTM C1186.

Water absorption coefficient (WAC) is also shown to be significantlyreduced in the preferred embodiments. FIG. 5 indicates water absorptionrates of two composite examples, 5 and 6. It has been found that adecrease in water absorption properties influence better performance infreeze thaw and shrinkage of the building material. The WAC test methodis based on ISO 15148:2002(E).

The preferred embodiment also improves the smoothness of the product bymore than 15%.

Various preferred embodiments of the present disclosure provide fibercement building materials with improved Modulus of Rupture (MOR),acceptable density range and lower moisture movement (MM) withcomparable performance in other criteria. In one embodiment, the fibercement building material has improved resistance to freeze and thaw andimproved dimensional stability compared to the materials made with 100%cellulose fibers, for example using 7-10% pulp content, as well as otherproperty enhancements, while maintaining the mechanical and physicalproperties such as nailability. This achievement was unexpected as thebrittleness of a higher cement containing composite was thought tohinder nailing capabilities.

Some embodiments of the present disclosure are directed to manufacture anew building material that contains a blend of cellulose fibers andpolypropylene fibers at preselected ratios. The formulation can be usedto produce fiber-reinforced cement composites with the Hatschekmanufacturing process. In the Hatschek process, a diluted aqueoussuspension is filled in the tub fitted with means for uniformlydistributing constituents within the tubs. A filter drum is partiallyimmersed in each tub and the rotation makes the deposition on the drumsurface to build up the thin film layer composed of fibers, aggregates,hydraulic binders and additives. The film is carried by a felt onto asize roller, where the film thickness is built up. It is then cut tounwind from the size roll and one sheet of fiber cement is formed. Thefiber cement sheet can be subsequently cured at a temperature up to 175°C. autoclave, preferably 160° C. and a pressure of about 75 psi withoutdegrading the fibers.

The embodiments illustrated and described above are provided as examplesof certain preferred embodiments of the present invention. Variouschanges and modifications can be made from embodiments presented hereinby those skilled in the art without departure from the spirit and scopeof this invention.

What is claimed is:
 1. A fiber cement composite material, comprising:about 10%-80% by weight cementitious binder; about 20%-80% by weightsilica; about 0%-50% by weight density modifier; about 0%-10% additives;and about 0.5%-20% by weight a 3-mode fiber blend, said fiber blendcomprising short and high surface cellulose fiber, medium length andsurface cellulose fiber and long and low surface synthetic fiber.
 2. Thefiber cement composite material of claim 1, wherein the synthetic fiberscomprises polypropylene fibers.
 3. The fiber cement composite materialof claim 2, wherein the polypropylene fibers have an average length ofbetween 4 mm-15 mm.
 4. The fiber cement composite material of claim 2,wherein the polypropylene fibers are engineered with a hydrophilicsurface and a hydrophobic bulk part.
 5. The fiber cement compositematerial of claim 1, wherein the percent by weight ratio of thecellulose fibers to the synthetic fibers is between 3 to
 24. 6. Thefiber cement composite material of claim 1, wherein the fiber blendcomprises refined shorter cellulose fibers, unrefined cellulose fibers,and long PP fibers, wherein the average length of the refined shorterfibers is less than the average length of the unrefined cellulosefibers, wherein the average length of the long PP fibers is greater thanthe average length of the unrefined cellulose fibers.
 7. The fibercement composite material of claim 6, wherein the fiber blend comprisesabout 60% to 80% refined shorter cellulose fibers having an averagelength of less than or equal to 2 mm, about 10% to 25% unrefinedcellulose fibers having an average length of between 2 to 3 mm, andabout 10 to 25% long PP fibers having an average length between 4 to 15mm.
 8. The fiber cement composite material of claim 1, wherein saidmaterial having a moisture movement (MM) of less than 0.5%.
 9. The fibercement composite material of claim 1, wherein the moisture movement ofthe composite material is at least 25% less than that of an equivalentfiber cement composite material containing no synthetic fibers.
 10. Afiber reinforced cement composition, comprising: a hydraulic binder;aggregates; cellulose fibers; and polypropylene fibers, saidpolypropylene fibers having irregular forms, wherein the ratio of thepercent by weight of cellulose fibers to polypropylene fibers is between3 to
 24. 11. The fiber reinforced cement composition of claim 10,wherein the composition comprises about 4% to 10% by weight cellulosefibers and about 0.25% to 2% polypropylene fibers.
 12. The fiberreinforced cement composition of claim 10, wherein the cellulose fiberscomprise refined shorter cellulose fibers and unrefined cellulosefibers.
 13. The fiber reinforced cement composition of claim 12, whereinthe ratio of the weight ratio of the refined shorter cellulose fibers tothe unrefined cellulose fibers is between 2.4 to
 8. 14. A method ofmanufacturing a fiber reinforced cementitious article, comprising:forming a fiber cement slurry, said fiber cement slurry comprises ahydraulic binder, aggregate, water, cellulose fibers and polypropylenefibers, wherein the percent weight ratio between the cellulose fibersand the polypropylene fibers is between 3 to 24; depositing said fibercement slurry on a plurality of sieve cylinders that are rotated throughthe fiber cement slurry, wherein the cellulose fibers and polypropylenefibers filter the fiber cement slurry to form a thin fiber cement film;transferring a series of sequential layers of the thin fiber cementfilms to a belt so as to build a thicker fiber cement layer; removingwater from the thicker fiber cement layer; and curing said thicker fibercement layer in an autoclave at a temperature of at least 150° C.